Xylene at a glance
iSolvents Chemicals
Xylene is an organic chemical compound that can easily be identified by its smell. Its chemical structure is typified by a central benzene ring of six carbon atoms. Two more methyl groups bound to either the first, second or fourth carbon of the ring explains why xylene has many structural isomers. In industry, it is mostly produced by the cracking of the natural gas naphtha, but there are new cost-effective methods by conversion from its isomers.
One of the isomers, Toluene, can undergo alkylation with methanol over an alumino-silicate zeolite catalyst producing mixtures of xylene that can be purified. As the toluene passes over the metal catalyst, its methyl groups are re-orientated around the benzene ring to form xylene (Tahir Ashraf et al, 2013).
Xylene is a colourless, flammable and slightly greasy liquid with a melting point at -48°C and a boiling point at 140°C. Compare its range of melting point to boiling point to that of water: 0°C-100°C. This explains why xylene can be stored at ambient temperatures below freezing. However, a distinctive chemical characteristic of xylene is that it degrades plastic materials. Some plastics show resistance at low temperatures but are broken down by xylene at higher temperatures. Therefore, xylene is best stored in metal containers.
p-xylene is the most desirable isomer in industry, showing increased demands in the market due to the textile industry. The growing demand for polyester fibers is sustainably supplied by p-xylene because of its energy efficiency in chemical processing. As it reacts it wastes less chemical energy as it converts into long-chain polymers (Shi et al, 2021).
Another day-to-day industry utility with xylene as a substrate, is the production of PET plastics. Similarly in this process, p-xylene is the base monomer that reacts to form complex polyethylene terephthalate (PET). PET plastic is the standard plastic used in almost any product, such as a plastic bottle. This emphasizes the significance of PET plastic production from xylene as it supplies the markets with an essential material. Research has shown that this PET can be biomass-derived, and with the same reaction of p-xylene it can produce a degradable plastic that is less harmful to the environment (Dutta & Bhat, 2020).
Xylene solutions are also used in biology labs for two purposes. It is used as an immersion oil in microscopy to protect the lenses of the microscope whilst bending the light rays that shine from underneath the specimen, allowing to focus an image. It is also used as a clearing agent for the preparation of histology slides.
Xylene is also used as a solvent in paint and cleaning products. It is also an ingredient in gasoline. It readily evaporates – thus making it a desirable base for paint so that it dries quicker than acrylic bases – but this may cause several health considerations. Under frequent inhalation, xylene depresses the central nervous system which causes dizziness, weakness, irritability, and vomiting. Upon long-term exposure it can cause hearing loss – this is known as chronic solvent-induced encephalopathy.
Effort should be made in keeping to health protocols in the lab or working environment. This is successful by a two-fold approach: educating technicians with the health hazards involved in handling xylene and providing personal protective equipment to workers who are frequently exposed to xylene for long periods of time (Kandyala et al, 2010).
Muhammad Tahir Ashraf, Rachid Chebbi, and Naif A. Darwish. Industrial & Engineering Chemistry Research 2013 52 (38), 13730-13737
Qian Shi, Jonathan C. Gonçalves, Alexandre F.P. Ferreira, Alírio E. Rodrigues. A review of advances in production and separation of xylene isomers.Chemical Engineering and Processing - Process Intensification. Volume 169. 2021. 108603. ISSN 0255-2701.
Dutta, S., Bhat, N.S. Catalytic synthesis of renewable p-xylene from biomass-derived 2,5-dimethylfuran: a mini review. Biomass Conv. Bioref. (2020).
Reena Kandyala, Sumanth Phani C Raghavendra, Saraswathi T Rajasekharan. Xylene: An overview of its health hazards and preventive measures. J Oral Maxillofac Pathol. 2010 Jan-Jun; 14(1): 1–5.